1. Field of the Invention
The present invention relates to data reproduction, and more particularly, to a data reproducing apparatus for and method of improving data detection performance by adjusting decision levels used in a data detector and a method.
2. Description of the Related Art
Technology related to a partial response maximum likelihood (PRML) has been developed to increase a recording density through signal processing without sharply changing the characteristics of conventional recording/reproducing apparatuses, and many specific means based on this technology have been proposed.
In FIG. 1, which is a block diagram illustrating a conventional data reproducing apparatus, an analog to digital converter (ADC) 100 samples an input radio frequency (RF) signal. A direct current (DC) offset compensator 102 and an adder 104 compensate for a DC offset component contained in the sampled RF data, and the compensated result is provided to an equalizer 106. A level error detector 108 detects an error ek between a target value and the output of the equalizer 106 composed of a finite impulse response (FIR) filter, based on the level of a minimum pit (or a mark)—3T (T: a bit space) in the case of a conventional digital versatile disc (DVD) or compact disc (CD).
Where an error value detected by the level error detector 108 is positive (+), a filter coefficient adjustor 110 determines that the level of the minimum pit is larger than the target value and adjusts a filter coefficient in a negative direction. The adjusted filter coefficient Wk+1 is provided to the equalizer 106 to decrease the output level of the minimum pit provided by the equalizer 106. Alternatively, where an error value detected by the level error detector 108 is negative (−), the filter coefficient adjustor 110 determines that the level of the minimum pit is smaller than the target value and adjusts a filter coefficient in a positive direction. The adjusted filter coefficient Wk+1 is provided to the equalizer 106 to increase the output level of the minimum pit provided by the equalizer 106.
With such an arrangement, the minimum pit having an appropriate level is output, thereby improving the performance of a Viterbi detector 112. In FIG. 1, xk denotes the input data of the equalizer 106, yk denotes the output data of the equalizer 106, and Wk+1 denotes the adjusted filter coefficient for the equalizer 106.
Meanwhile, the DC offset compensator 102 accumulates +1 where a sampled value Sk from the ADC 100 which samples an input RF signal exceeds zero and −1 where the sampled value Sk is smaller than zero. Where the accumulated value is equal to or larger than a predetermined positive (+) threshold, the DC offset compensator 102 decreases the sampled value Sk by one level (½(n−1) in the case of n-bit sampling) using a level compensation value Lk to compensate the sampled value Sk. Where the accumulated value is smaller than a predetermined negative (−) threshold, the DC offset compensator 102 increases the sampled value Sk by one level using a level compensation value Lk to compensate the sampled value Sk.
A DC offset is removed from the RF signal through such an arrangement. However, for example, if asymmetry occurs in the RF signal, a large error occurs between output data of the equalizer 106 and a decision level required by the Viterbi detector 112 even if the filter coefficient adjustor 110 detects an optimal FIR filter coefficient. Here, the decision level indicates the magnitude of a predicted sample value used in a branch metric operational unit of the Viterbi detector 112.
Accordingly, where a RF signal is distorted due to asymmetry and disc skew, the detection performance of a Viterbi detector is lowered even if equalization is performed using an optimal FIR filter coefficient.